Level 1 staff starts at 2000 and goes up by 1% per week, plus you pay the final week's salary on firing them.
So after one season (14 weeks), their weekly salary is up to $2298 and firing them then would have a payback of 8 weeks.
If you fired them after 10 weeks, their weekly salary is up to $2209 and firing them would have a payback of 11 weeks.
So you break even firing them every 11 weeks at a salary of $2231, saving about $500 over the course of the next 11 weeks.
*Math credit goes to Azariah*